Conventionally, the adhering method used for forming an automobile interior part has widely employed a method of spray-coating an adherend with a two pack type solvent adhesive. However, such a method is not desirable in working environment because an organic solvent and the like used as the solvent is diffused during spray-coating or drying of the adhesive. Such a method may affect external environment when, for example, the solvent leaks to the outside of a workplace. To address this, the method causes a problem of requiring equipment and the like for recovering the solvent. The method has other problems. The solvent adhesive is a liquid. Hence, the adhesive that is applied on any other area than an adherend is difficult to be recovered and the method increases spray loss. Furthermore, the two pack type adhesive that remains in a tank is required to be discarded and the inside of the tank is required to be washed with an organic solvent, for example, at the end of daily operation. Hence, the method causes material loss. Moreover, these substances are required to be disposed of as industrial waste products.
As a method for improving these problems, various adhesives and the like have been developed (Patent Documents 1 to 4).
Patent Document 1 discloses a one pack type chloroprene adhesive composition rather than the two pack type, but the environmental issues are not improved because the composition is a solvent adhesive. Patent Document 2 discloses an aqueous adhesive rather than the solvent adhesive. However, the adhesive is a two pack type adhesive to leave the problems of material loss and the like, and also the adhesive is an aqueous adhesive to cause a problem of taking long time for drying. Patent Document 3 discloses a hot melt adhesive rather than the solvent adhesive. The adhesive has a short open time after coating of the adhesive to cause a problem of material loss during coating. Patent Document 4 discloses a precoated surface material for an automobile interior in which a hot melt adhesive is previously applied to the back surface of an automobile interior surface material. The adhesive is a precoated type and is previously applied to the surface material. Hence, the adhesive has a problem of material loss when, for example, an unnecessary part is cut off.
Meanwhile, in the field of coating technology, a powder coating is used. A carbodiimide compound and the like are disclosed as a curing agent for the powder coating (Patent Document 5), and an electrostatic powder coating method that enables the adhesion of an acrylic powder coating to the surface of an aluminum wheel is disclosed (Patent Document 6). However, for the application to adhesion technology, especially for the application to automobile interior parts, there are some problems in heat tolerance (including heat tolerance in a high temperature environment. Hereinafter the same applies), adhesion strength, and the like that should be solved. Such an application is not easy under present circumstances.
In the field of thermosetting compositions that are used for adhesives and the like, from the viewpoint of satisfying both cold curability and storage stability, there is disclosed a thermosetting composition including a mixture of a particular urethane prepolymer and a fine powder coated amine in which active amino groups on a surface are covered (Patent Documents 7 and 8). However, in the thermosetting composition described in Patent Documents 7 and 8, as the fine powder for covering the active amino group, in Examples, the fine powder used for the coated amine is exemplified by titanium oxide, hydrophobic silica, and polyvinyl chloride alone. Furthermore, the present inventors have studied to reveal problems in the storage stability. For example, the thermosetting composition may form aggregates due to heat (temperature effect at room temperature) or humidity during a long-term storage even when titanium oxide is used, and the formed aggregate is difficult to be re-powdered. Thus, such a composition may interfere with spray-coating of an adherend or may inhibit the curing reaction (hereinafter, also referred to as blocking).